This invention relates to high pressure curing of elastomeric articles by expanding an elastic bladder member or the like against the article and thereby causing it to flow in a softened state against a contoured mold surface.
Various fluids have been used or proposed in the past for pressurizing an elastic bladder against the article to be vulcanized. The most prominent systems use either all steam or hot water curing mediums. The use of an inert gas either by itself or preceding the introduction of steam is also known, see, for instance, U.S. Pat. Nos. 661,178 to Hill, Jr., 676,350 to Bourn, 1,746,357 to Minor, and 1,871,120 to Denmire. In these applications the inert gas was used primarily in lieu of air or steam to prevent oxidation of the bladder member. The pressures disclosed in these prior art methods were generally considerably less than about 200 psi.
While these prior art curing methods have been more or less satisfactory for their specific purposes there exist certain problems which these methods do not address. One such problem, which is especially characteristic when using steam as a curing medium, is the failure to produce a balanced or uniform cure throughout the article being vulcanized; this is particularly evident when the article to be vulcanized has a non-uniform cross-sectional thickness at different locations along the article. In practice this problem is evidenced in the curing of tires which normally have a greater shoulder gauge than sidewall gauge, resulting quite often in over-curing the thinner portions of the cross-section and/or undercuring the thicker portions, with a significant reduction in tire road performance and mileage.
Another apparent problem which has been prevalent is that for many applications there has been insufficient adhesion between the elastomeric body of an article and its associated embedded reinforcement. This problem evidences itself in the field of high performance power transmission belting. This belting is often built up on a mandrel by applying layers of fabric and/or rubber over which is helically wound tensile cord in the form of a corded textile material or inorganic filament. A rubber containing layer is then applied over the reinforcement with or without a cover and the sleeve of belting is cured and individual endless belts are cut from the sleeve. Raw edge V-belts made in this manner may have severed edge cord ends exposed along the driving surfaces of the belt which have a tendency to delaminate and separate, leading to failure of the belt prematurely. The edge cord failure is believed to be at least partially caused by inadequate bonding to the rubber matrix.
The present invention has for its primary object the provision of a method for curing elastomeric articles which is both efficient and economical and which produces an article which is uniformly cured at higher than conventional pressures and is characterized by improved adhesion between the elastomeric body and any reinforcement which may be contained therein.